BSByteStream.h

//C- -*- C++ -*-//C- -------------------------------------------------------------------//C- DjVuLibre-3.5//C- Copyright (c) 2002 Leon Bottou and Yann Le Cun.//C- Copyright (c) 2001 AT&T//C-//C- This software is subject to, and may be distributed under, the//C- GNU General Public License, Version 2. The license should have//C- accompanied the software or you may obtain a copy of the license//C- from the Free Software Foundation at http://www.fsf.org .//C-//C- This program is distributed in the hope that it will be useful,//C- but WITHOUT ANY WARRANTY; without even the implied warranty of//C- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the//C- GNU General Public License for more details.//C- //C- DjVuLibre-3.5 is derived from the DjVu(r) Reference Library//C- distributed by Lizardtech Software. On July 19th 2002, Lizardtech //C- Software authorized us to replace the original DjVu(r) Reference //C- Library notice by the following text (see doc/lizard2002.djvu)://C-//C- ------------------------------------------------------------------//C- | DjVu (r) Reference Library (v. 3.5)//C- | Copyright (c) 1999-2001 LizardTech, Inc. All Rights Reserved.//C- | The DjVu Reference Library is protected by U.S. Pat. No.//C- | 6,058,214 and patents pending.//C- |//C- | This software is subject to, and may be distributed under, the//C- | GNU General Public License, Version 2. The license should have//C- | accompanied the software or you may obtain a copy of the license//C- | from the Free Software Foundation at http://www.fsf.org .//C- |//C- | The computer code originally released by LizardTech under this//C- | license and unmodified by other parties is deemed "the LIZARDTECH//C- | ORIGINAL CODE." Subject to any third party intellectual property//C- | claims, LizardTech grants recipient a worldwide, royalty-free, //C- | non-exclusive license to make, use, sell, or otherwise dispose of //C- | the LIZARDTECH ORIGINAL CODE or of programs derived from the //C- | LIZARDTECH ORIGINAL CODE in compliance with the terms of the GNU //C- | General Public License. This grant only confers the right to //C- | infringe patent claims underlying the LIZARDTECH ORIGINAL CODE to //C- | the extent such infringement is reasonably necessary to enable //C- | recipient to make, have made, practice, sell, or otherwise dispose //C- | of the LIZARDTECH ORIGINAL CODE (or portions thereof) and not to //C- | any greater extent that may be necessary to utilize further //C- | modifications or combinations.//C- |//C- | The LIZARDTECH ORIGINAL CODE is provided "AS IS" WITHOUT WARRANTY//C- | OF ANY KIND, EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED//C- | TO ANY WARRANTY OF NON-INFRINGEMENT, OR ANY IMPLIED WARRANTY OF//C- | MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.//C- +------------------------------------------------------------------// // $Id: BSByteStream.h,v 1.8 2003/11/07 22:08:20 leonb Exp $// $Name: debian_version_3_5_17-3 $#ifndef _BSBYTESTREAM_H#define _BSBYTESTREAM_H#ifdef HAVE_CONFIG_H#include "config.h"#endif#if NEED_GNUG_PRAGMAS# pragma interface#endif/** @name BSByteStream.h Files #"BSByteStream.h"# and #"BSByteStream.cpp"# implement a very compact general purpose compressor based on the Burrows-Wheeler transform. The utility program \Ref{bzz} provides a front-end for this class. Although this compression model is not currently used in DjVu files, it may be used in the future for encoding textual data chunks. {\bf Algorithms} --- The Burrows-Wheeler transform (also named Block-Sorting) is performed using a combination of the Karp-Miller-Rosenberg and the Bentley-Sedgewick algorithms. This is comparable to (Sadakane, DCC 98) with a slightly more flexible ranking scheme. Symbols are then ordered according to a running estimate of their occurrence frequencies. The symbol ranks are then coded using a simple fixed tree and the \Ref{ZPCodec} binary adaptive coder. {\bf Performances} --- The basic algorithm is mostly similar to those implemented in well known compressors like #bzip# or #bzip2# (\URL{http://www.muraroa.demon.co.uk}). The adaptive binary coder however generates small differences. The adaptation noise may cost up to 5\% in file size, but this penalty is usually offset by the benefits of adaptation. This is good when processing large and highly structured files like spreadsheet files. Compression and decompression speed is about twice slower than #bzip2# but the sorting algorithms is more robust. Unlike #bzip2# (as of August 1998), this code can compress half a megabyte of "abababab...." in bounded time. Here are some comparative results (in bits per character) obtained on the Canterbury Corpus (\URL{http://corpus.canterbury.ac.nz}) as of August 1998. The BSByteStream performance on the single spreadsheet file #Excl# moves #bzz#'s weighted average ahead of much more sophisticated methods, like Suzanne Bunton's #fsmxBest# system \URL{http://corpus.canterbury.ac.nz/methodinfo/fsmx.html}. This result will not last very long. {\footnotesize \begin{tabular}{lccccccccccccc} & text & fax & Csrc & Excl & SPRC & tech & poem & html & lisp & man & play & Weighted & Average \\ compress & 3.27 & 0.97 & 3.56 & 2.41 & 4.21 & 3.06 & 3.38 & 3.68 & 3.90 & 4.43 & 3.51 & 2.55 & 3.31 \\ gzip -9 & 2.85 & 0.82 & 2.24 & 1.63 & 2.67 & 2.71 & 3.23 & 2.59 & 2.65 & 3.31 & 3.12 & 2.08 & 2.53 \\ bzip2 -9 & 2.27 & 0.78 & 2.18 & 1.01 & 2.70 & 2.02 & 2.42 & 2.48 & 2.79 & 3.33 & 2.53 & 1.54 & 2.23 \\ ppmd & 2.31 & 0.99 & 2.11 & 1.08 & 2.68 & 2.19 & 2.48 & 2.38 & 2.43 & 3.00 & 2.53 & 1.65 & 2.20 \\ fsmx & {\bf 2.10} & 0.79 & {\bf 1.89} & 1.48 & {\bf 2.52} & {\bf 1.84} & {\bf 2.21} & {\bf 2.24} & {\bf 2.29} & {\bf 2.91} & {\bf 2.35} & 1.63 & {\bf 2.06} \\ {\bf bzz} & 2.25 & {\bf 0.76} & 2.13 & {\bf 0.78} & 2.67 & 2.00 & 2.40 & 2.52 & 2.60 & 3.19 & 2.52 & {\bf 1.44} & 2.16 \end{tabular} } Note that the DjVu people have several entries in this table. Program #compress# was written some time ago by Joe Orost (\URL{http://www.research.att.com/info/orost}). The #ppmc# method, (a precursor of #ppmd#) was created by Paul Howard (\URL{http://www.research.att.com/info/pgh}). The #bzz# program is just below your eyes. @author L\'eon Bottou <leonb@research.att.com> -- Initial implementation\\ Andrei Erofeev <eaf@geocities.com> -- Improved Block Sorting algorithm. @memo Simple Burrows-Wheeler general purpose compressor. @version #$Id: BSByteStream.h,v 1.8 2003/11/07 22:08:20 leonb Exp $# *///@{#include "ByteStream.h"#include "GException.h"#include "ZPCodec.h"#ifdef HAVE_NAMESPACESnamespace DJVU {
# ifdef NOT_DEFINED // Just to fool emacs c++ mode}
#endif#endif/** Performs bzz compression/decompression. Class #BSByteStream# defines a \Ref{ByteStream} which transparently performs the BZZ compression/decompression. The constructor of class \Ref{BSByteStream} takes another \Ref{ByteStream} as argument. Any data written to the BSByteStream is compressed and written to this second ByteStream. Any data read from the BSByteStream is internally generated by decompressing data read from the second ByteStream. Program \Ref{bzz} demonstrates how to use this class. All the hard work is achieved by a simple ByteStream to ByteStream copy, as shown below. \begin{verbatim} GP<ByteStream> in=ByteStream::create(infile,"rb"); GP<ByteStream> out=ByteStream::create(outfile,"wb"); if (encoding) { BSByteStream bsb(out, blocksize); bsb.copy(*in); } else { BSByteStream bsb(in); out->copy(bsb); } \end{verbatim} Due to the block oriented nature of the Burrows-Wheeler transform, there is a very significant latency between the data input and the data output. You can use function #flush# to force data output at the expense of compression efficiency. You should never directly access a ByteStream object connected to a valid BSByteStream object. The ByteStream object can be accessed again after the destruction of the BSByteStream object. Note that the encoder always flushes its internal buffers and writes a few final code bytes when the BSByteStream object is destroyed. Note also that the decoder often reads a few bytes beyond the last code byte written by the encoder. This lag means that you must reposition the ByteStream after the destruction of the BSByteStream object and before re-using the ByteStream object (see \Ref{IFFByteStream}.)*/00199class BSByteStream : publicByteStream
{
public:
// Limits on block sizesenum { MINBLOCK=10, MAXBLOCK=4096 };
// Sorting tresholdsenum { FREQMAX=4, CTXIDS=3 };
class Decode;
class Encode;
protected:
BSByteStream(GP<ByteStream> bs);
public: /** Creates a BSByteStream. The BSByteStream will be used for decompressing data. \begin{description} \item[Decompression] The BSByteStream is created and the decompressor initializes. Chunks of data will be read from ByteStream #bs# and decompressed into an internal buffer. Function #read# can be used to access the decompressed data. \end{description} */staticGP<ByteStream>create(GP<ByteStream> bs);
/** Constructs a BSByteStream. The BSByteStream will be used for compressing data. \begin{description} \item[Compression] Set #blocksize# to a positive number smaller than 4096 to initialize the compressor. Data written to the BSByteStream will be accumulated into an internal buffer. The buffered data will be compressed and written to ByteStream #bs# whenever the buffer sizes reaches the maximum value specified by argument #blocksize# (in kilobytes). Using a larger block size usually increases the compression ratio at the expense of computation time. There is no need however to specify a block size larger than the total number of bytes to compress. Setting #blocksize# to #1024# is a good starting point. A minimal block size of 10 is silently enforced. \end{description} */staticGP<ByteStream>create(GP<ByteStream> bs, constint blocksize);
// ByteStream Interface
~BSByteStream();
virtuallongtell(void) const;
virtualvoidflush(void) = 0;
protected:
// Datalong offset;
int bptr;
unsignedint blocksize;
intsize;
ByteStream *bs;
GP<ByteStream> gbs;
unsignedchar *data;
GPBuffer<unsigned char> gdata;
// CoderGP<ZPCodec> gzp;
BitContext ctx[300];
private:
// Cancel C++ default stuffBSByteStream(constBSByteStream &);
BSByteStream & operator=(constBSByteStream &);
BSByteStream(ByteStream *);
BSByteStream(ByteStream *, int);
};
//@}#ifdef HAVE_NAMESPACES}
# ifndef NOT_USING_DJVU_NAMESPACEusing namespace DJVU;
# endif#endif#endif